It is worth mentioning that when cleansed the plants will stay that way for something like 2 hours. Their quests can only be completed like every 10-15 minutes though. This means you can get these buffs/items pretty consistently for 16 levels (the starter quest can be accepted at level 48, and the buffs continue to give the buff through 63) as long as you aren't dying very frequently and you actually do enough quests in felwood to keep your cenarion salve in stock (don't throw away any corrupted soul shards)

Du baume par la pioche

Progrès

If you possess a Cenarion beacon while mining in Felwood, you will be able to see tainted vitriol that corrupts a vein of raw metal. I know how to purify that vitriol and turn it into a reagent that goes into making Cenarion plant salve. You will then use that salve on plants you find in the wild that need saving.

If you have collected any tainted vitriol, I'll give you some Cenarion plant salve I have already prepared.